North Korea Says "hello", while Trump and Abe were Golfing

Yesterday, while Trump Japanese PM Abe were golfing at the Mar-a-Lago, Mr. Trump’s club in Palm Beach, North Korea launched a ballistic missile toward the sea off its eastern coast on Sunday, in what South Korea called the North’s first attempt to test President Trump’s policy on the isolated country.

In response, Mr. Trump and Mr. Abe hastily arranged a joint appearance, in which the Japanese PM address the audience first , saying “North Korea’s most recent missile launch is absolutely intolerable,”

Looking grim, Mr. Trump said nothing about the missile launch, but pledged to staunchly back Japan. “I just want everybody to understand and fully know that the United States of America stands behind Japan, its great ally, 100 percent,” he said.

https://www.nytimes.com/2017/02/11/world/asia/north-korea-missile-test-trump.html?_r=0
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Team Trump has not announced that the US will put North Korea "on notice" ; it did that immediately after Iran had tested launched a missile on 2 Feb 2017. As for his early morning Tweet, this AM, while he teased about Mark Cuban, he did not comment on North Korea's missile testing.

On the heels of Trump re-affirming the "one china" policy, at the request of Chinese President Xi, how worried should Japan be?